A magnetic field is created in a material when the spins of the atoms all point in the same direction. With non-magnetic materials, the spins are undirected and their effects cancel each other out.

About 50 years ago, it was theoretically postulated that a magnetic moment can also occur temporarily in a non-magnetic material [1]. This moment is formed by so-called spin excitons. These are short-lived quasiparticles that arise from the interaction of electrons. Normally, these spin excitons disappear very quickly. However, the theory says that many of them can stabilize each other and then catalyze the emergence of even more spin excitons. So far, this has not been observed experimentally.

L. Andrew Wray, New York University, USA, and colleagues have shown by means of X-ray scattering, neutron scattering, and accompanying modeling that magnetic exciton fields occur at comparatively high temperatures in the uranium antimony compound USb₂. USb₂ has disordered spins and is usually not magnetic.

According to the researchers, this uranium compound could be the first example of such an exciton magnet above ultracold conditions, a so-called singlet ground state magnet. This would be proof that the theory of singlet-based magnetism is correct. In addition, this finding could be useful for new types of magnetic data storage for computers.

• High temperature singlet-based magnetism from Hund’s rule correlations,
  Lin Miao, Rourav Basak, Sheng Ran, Yishuai Xu, Erica Kotta, Haowei He, Jonathan D. Denlinger, Yi-De Chuang, Y. Zhao, Z. Xu, J. W. Lynn, J. R. Jeffries, S. R. Saha, Ioannis Giannakis, Pegor Aynajian, Chang-Jong Kang, Yilin Wang, Gabriel Kotliar, Nicholas P. Butch, L. Andrew Wray,
  Nat. Commun. 2019.
  https://doi.org/10.1038/s41467-019-08497-3

Reference

• [1] Collective Excitations and Magnetic Ordering in Materials with Singlet Crystal-Field Ground State,
  Yung-Li Wang, Bernard R. Cooper,
  Phys. Rev. 1968, 172, 539–551.
  https://doi.org/10.1103/PhysRev.172.539